Comparative morphology and ontogenetic patterns of Bdallophytum species (Cytinaceae, Malvales): insight into the biology of an endoparasitic genus

Abstract

Cytinaceae are root endoparasitic plants with only three genera. Their biology is largely unknown, and most knowledge of the family is based on the Old World genus Cytinus. Here, we studied all three species of the New World Bdallophytum from Mexico. We describe their morphoanatomy, floral development, and embryology, highlighting the unique traits of Bdallophytum compared with two other genera of the family and members of Malvales. Both B. americanum and B. andrieuxii are dioecious, whereas B. oxylepis is gynomonoecious. The floral size and the number of floral organs vary within and among species, which appears to be common in Cytinaceae. The flowers of Bdallophytum exhibit synorganization in sexual organs, a synandrium in male flowers, and a gynostemium in bisexual flowers of B. oxylepis. Unisexual and bisexual flowers are zygomorphic at the early developmental stages. The unisexual flowers become actinomorphic in later development, while the bisexual flowers of B. oxylepis remain zygomorphic. The androecium of Bdallophytum has key traits shared with some Malvales, such as the fused filaments in Malvaceae and Sarcolaenaceae and the connective appendage shared with Dipterocarpaceae. Our results suggest that a unitegmic ovule is a unique trait for Bdallophytum. This is proposed here as a putative synapomorphy for Bdallophytum.